You're on the right track. Think of horizontal shifting this way: suppose I have a function, x^2. It's zero when x = 0, right? Now suppose I shift it horizontally. That always looks like replacing the x with an x-a or x+a. So which is which? Well, if I replace x with x-2 in our function, then I get (x-2)^2. When is that zero? When x = 2. Evidently, then, the x-2 shifting is to the right. If I were to do x+2, then I'd have (x+2)^2, which is zero when x = -2. So that one's shifted to the left.